A twin fall davit lifeboat or a totally enclosed motor propelled survival craft is used to evacuate personnel from an offshore oil drilling platform or a marine vessel. This type of lifeboat system has release mechanisms that disengage the lifeboat from the davit lines when the craft reaches or is just above the water. Regulations state that the release mechanisms on a lifeboat must be operable with the full weight of the lifeboat on the davit lines. Although this regulation has been drafted to ensure that a lifeboat will be positively released when the release mechanisms are operated, there has been and continues to be, isolated cases of malfunctions of the release mechanisms, including cases of premature releases at some undesirable distance above the water.
Generally, the lifeboat release mechanisms of the prior art have interlocking parts including hooks to which are attached the ropes supporting the lifeboat. These hooks are allowed to pivot in such a way as to release the ropes of the lifeboat upon a rotation thereof from their holding positions. Each hook is held in its holding position by a catch member. In some of the prior art devices, the engagement of the hook with the catch member is very small such that when the catch member is moved even by a slight amount, the hook is released and pivots on itself, thereby releasing the lifeboat line unexpectedly.
Examples of lifeboat release mechanisms of the prior art are shown in the following documents:    U.S. Pat. No. 60,963 issued to James R. Taylor on Jan. 1, 1867;    U.S. Pat. No. 60,964 issued to James R. Taylor on Jan. 1, 1867;    U.S. Pat. No. 60,965 issued to James R. Taylor on Jan. 1, 1867;    U.S. Pat. No. 60,966 issued to James R. Taylor on Jan. 1, 1867;    U.S. Pat. No. 61,279 issued to James R. Taylor on Jan. 15, 1867;    U.S. Pat. No. 61,280 issued to James R. Taylor on Jan. 15, 1867;    U.S. Pat. No. 61,281 issued to James R. Taylor on Jan. 15, 1867;    U.S. Pat. No. 1,030,586 issued to J. Irwin on Jun. 25, 1912;    U.S. Pat. No. 2,618,792 issued to A. Vreugdenhil on Nov. 25, 1952;    U.S. Pat. No. 4,201,410 issued to H. Crawford et al. on May 6, 1980;    U.S. Pat. No. 4,358,146 issued to C. A. Goudey on Nov. 9, 1982;    U.S. Pat. No. 4,610,474 issued to J. Jaatinen on Sep. 9, 1986.
In the devices of U.S. Pat. No. 1,030,586 and U.S. Pat. No. 4,358,146, in particular, the catch members are held in a holding position by cams and springs. In another type, as illustrated and described in U.S. Pat. No. 4,201,410, a pair of levers must be pulled in sequence with each other to release the catch member. The device of U.S. Pat. No. 4,610,474 has an hydraulic cylinder which is used to retain a catch member in its holding position.
A lifeboat is exposed to sea water and harsh weather conditions. The lifeboat and its release mechanisms are repainted periodically to limit their deterioration by corrosion. During winter, a layer of ice accumulates on every part of a lifeboat and on its release mechanisms. Therefore a release mechanism must be operable when covered with ice, when partly corroded and after having been repainted several times.
Because of their exposure to the elements, these lifeboat release mechanisms should not contain small springs, roller bearings, small gears, small levers and pins, sprockets and chains, hydraulic or pneumatic equipment, or other mechanical parts which are susceptible to seize in a corrosive environment or to jam when covered with ice.
Another preferred feature of a lifeboat release mechanism is that the engaging surfaces thereof should be as large as possible to prevent wear of its components after several years in service. The engagement surfaces between the latch members and the catch members in the release mechanisms of the prior art are often very small, such as a roller held against a relatively flat surface. A lifeboat suspended to a twin fall davit is often in motion from the force of the wind and the rocking of the vessel to which it is attached. Also, the vibrations of the engine of the vessels and of its propellers are transmitted through the vessel and into the release mechanisms of the lifeboat. These vibrations and the oscillatory motion of the lifeboat eventually wear out the engaging surfaces of the components of the release mechanisms, and where a hard roller bears against a flat surface, a flat spot is formed on the roller, or a notch is formed in the flat surface. It is believed that this type of wear in a lifeboat release mechanism is often the cause of malfunction of the release mechanism.
Accordingly, it may be appreciated that there continues to be a need for a new and improved lifeboat release mechanism that has a predictable unlatching movement, that contains no springs or similar small parts and that has large engagement surfaces of its elements to avoid localized wear.